1. Field of the Invention
The present invention relates generally to a dynamic damper and particularly to a dynamic damper for a hollow drive shaft of an automotive vehicle.
2. Related Art Statement
It is conventional that a drive shaft of an automotive vehicle is equipped with a dynamic damper for absorbing or attenuating vibration transmitted from a power unit to a vehicle body and preventing lowering of strength of the drive shaft due to metal fatigue thereof. Generally, a conventional dynamic damper includes a cylindrical damper mass member located outside a drive shaft with a suitable clearance provided therebetween, and elastic support means disposed between opposed surfaces of the drive shaft and damper mass for connecting the damper mass to the drive shaft and thereby elastically supporting the damper mass.
Meanwhile, there is a tendency that a conventional solid drive shaft is replaced with a hollow drive shaft which includes a tubular portion having a hollow bore inside. A hollow drive shaft is lighter than a solid drive shaft, and at the same time has flexural and torsional rigidities comparable to those of the solid drive shaft. Therefore, the use of a hollow drive shaft leads to lightening the overall weight of an automotive vehicle.
However, a hollow drive shaft has an outer diameter greater than that of a solid drive shaft. For applying the above-indicated conventional dynamic damper to a hollow drive shaft, it is necessary to adapt the damper mass to have a greater outer diameter, which leads to increasing the overall size of the dynamic damper. However, the enlarged dynamic damper needs widening of space for provision thereof.
In addition, when the damper mass having the increased outer diameter is rotated about the rotation axis thereof, the damper mass produces increased inertia force in the circumferential direction thereof. This means that, when torsional vibration is applied to the damper mass or dynamic damper, increased vibrational load is inputted to the elastic support means of the dynamic damper. This results in extreme reduction in durability of the elastic support means and thus the dynamic damper.